A unit cell of calcium fluoride has four calcium ions. The number of fluoride ions in the unit cell is

Options

A. 2
B. 4
C. 6
D. 8

Explanation

To determine the number of fluoride ions in the unit cell of calcium fluoride (CaF2), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Chemical Formula**: The chemical formula for calcium fluoride is CaF2. This indicates that for every calcium ion (Ca²⁺), there are two fluoride ions (F⁻).

2. **Identify the Number of Calcium Ions**: According to the question, the unit cell contains 4 calcium ions.

3. **Calculate the Number of Fluoride Ions**: Since each calcium ion is associated with 2 fluoride ions, we can calculate the total number of fluoride ions in the unit cell:
\[ \text{Number of Fluoride Ions} = \text{Number of Calcium Ions} \times 2 \]
Substituting the known value:
\[ \text{Number of Fluoride Ions} = 4 \times 2 = 8 \]

4. **Conclusion**: Therefore, the number of fluoride ions in the unit cell of calcium fluoride is 8.

### Final Answer:
The number of fluoride ions in the unit cell is **8**.

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